WO03/023890 describes hydrophilic polymers and their use in electrochemical cells. The hydrophilic polymers disclosed therein are obtainable by copolymerisation of hydrophobic and hydrophilic monomers that give a hydrophilic polymer a polymerisation. That publication also discloses the formation of membrane electrode assemblies in situ. WO2005/124893 and WO2007/105004 disclose composite membranes for use in electrochemical cells. Such materials have been produced by polymerising liquid monomers via gamma or thermal means.